This invention relates to fencing systems and to materials which comprise the various components of such systems.
Fence materials are generally selected on the basis of initial and estimated maintenance costs, durability, strength, safety and appearance. The fencing material that has been most widely used due to its low cost of installation and up-keep is metal wire, both smooth and barbed.
However, wire fencing, and particularly barbed wire fencing suffers from the disadvantage that it can cause painful, unsightly and life-threatening injury to valuable livestock, particularly when the stock becomes agitated or disturbed, as frequently happens during storms, or in the event predators penetrate the area in which the livestock are confined. The problem is compounded by the fact that wire fencing, whether it be barbed wire or smooth wire, is very thin and difficult to see and, as a result, animals are correspondingly more apt to contact wire fences than other more visible fences, such as wood rail fences. Wire fencing is also generally regarded as having poor aesthetic qualities, and it tends to rust or corrode after a few years of service.
For enclosing or confining certain types of livestock, such as thoroughbred race horses or animals of similar value, wood fences have also been employed. While pleasing to the eye and relatively safe, wood fences are nevertheless expensive to install and maintenance costs are particularly high. Wood fences also have the disadvantage of causing serious and, sometimes, fatal injuries to animals.
In an effort to retain the visibility and pleasing aesthetics of wood fencing, and the low cost and maintenance of wire fencing, it has been proposed to construct fences of wire webbing with wooden boards meshed therein. However, the durability of these fences is limited again by cost and by the tendency of the wood to weather and rot.
It is also known in the prior art to use plastic rather than wood to increase durability and to decrease the cost of fencing. For example, U.S. Pat. No. 3,877,140 discloses a picket fence composed of metal and plastic. The fence described there is well suited for applications not requiring a great deal of strength, such as for snow fencing, but is not particularly suited to applications where strength is of considerable importance, such as for the confinement of livestock.
Despite such attempted improvements, the most common practice still is to utilize plain or barbed wire wherein single strands of wire are, in effect, substituted for wooden rails, slats, and the like. One other advantage of wire fencing is that it may be made to be electrically conductive so as to provide low voltage electrical shocks on contact. U.S. Pat. No. 3,669,413, for example, discloses a metallic electrical fence comprising spaced, insulated fence posts supporting, via L-shaped tabs, one or more elongated current-carrying uninsulated conductor wires supplied with electrical current from a remote source.
In U.S. Pat. No. 3,516,643, a fence for livestock use is disclosed utilizing a plurality of non-electrified wires in combination with a single, uncoated electrically-conductive wire supported on insulators attached via extension means to fence posts.
U.S. Pat. No. 3,350,066 discloses still another wire fence construction wherein spaced, weighted fence posts support a plurality of horizontal, non-coated wires which may be electrified or non-electrified. A plurality of spring-biased wire engaging hooks tightly clamp the wires to the fence posts.
In U.S. Pat. No. 3,223,796, an insulated, electrically-conductive fence wire structure is described wherein a single strand of wire is supported between spaced fence posts. The reference discloses a copper or other highly-conductive wire loosely encased in a rubber or other flexible insulating material sleeve. Since the patent discloses the use of only a single wire and since the wire is made of a relatively soft metal (e.g., copper), serious doubts exist as to its usefulness in confining animals, particularly large ones (such as horses or cattle). The reference also discloses that the conductive wire may be covered with a substantially solid insulation coating 1/8 to 3/16 of an inch in thickness. The reference shows "conventional post connectors" that appear to fixedly hold the wire to the posts.
Also representative of known wire fence installations is a booklet published by United States Steel Corp. in 1980 entitled "How to Build Fences With USS Max-10 200 High Tensile Fence Wire". The booklet describes wire fence constructions utilizing varying numbers of smooth uncoated high-tensile wires connected to spaced fence posts by standard staple-type fasteners. Electrified versions are also described, utilizing insulated fasteners and short sections of tubular post insulators that loosely surround the wires.
Taking a different approach to conventional wire fencing, U.S. Pat. No. 4,111,399 discloses a fence comprising spaced fence posts supporting a series of horizontal as well as vertical strands of heavy gage wire. According to the reference, intermediate horizontal strands and all of the vertical strands are of a common gage, while the bottom and top horizontal strands are of a heavier gauge. In addition, the vertical spacing from top to bottom is varied, the lower horizontal strands closer together than the upper horizontal strands. All horizontal strands are secured to the posts using standard staple-type fasteners.
All of the above prior art wire fence constructions are unsatisfactory from the stand point that they lack aesthetic appeal, and they are oftentimes difficult to detect by livestock, horses or other animals by reason of the very small cross-sectional area of the individual wires. As previously indicated, the poor visibility associated with plain or barbed wire fences can lead to painful injury to the animals.
In my earlier U.S. Pat. No. 4,465,263, a composite metal and plastic fence system is disclosed which retains the visibility and attractiveness of wood fencing, but which has the high strength, low cost, low maintenance characteristics of wire fencing. The fence utilizes plastic webs reinforced by at least a pair of wires having high-tensile strength. In the preferred embodiment, the reinforcing wires are located at the upper and lower edges of the plastic web. In addition, installation of the fencing material is greatly facilitated by the use of uniquely configured brackets which provide vertical support for the webs.
In my co-pending parent application Ser. No. 643,008, various improvements in the earlier patented fence system are described which enable more effective and rapid installation of the fence. In one embodiment, a bracket is provided which not only encloses the wire reinforced plastic webbing, but also supports one or more low voltage conductive wires. In my other co-pending parent application Ser. No. 892,042, I disclose a fence system layout with concrete footings.
This invention relates to an improved wire strand for use not only in my prior metal and plastic composite fence systems, but also for use in a new wire strand fence system which overcomes the disadvantages of prior art wire fences. To this end, a composite strand is utilized which includes a high tensile strength elongated core member encased in a relatively thick coating of plastic material. The core member may be smooth, high-tensile strength steel wire, wire cable, glass fiber or synthetic fibers such as polyester, nylon polyester, polypropylene rope or cable, etc. The plastic coating or sheath may be polyvinyl chloride, polypropylene and rubber, or other thermoplastic olefin polymers or similar materials.
Various conventional techniques may be employed to encase the core member within the plastic sheath. In one exemplary embodiment, the plastic is extruded onto the core material so that the plastic is fixed to the strand, i.e., there is no relative sliding motion therebetewen. Extruding plastic coatings onto wire strands is not in itself new, and reference is made to U.S. Pat. No. 4,182,382, which discloses a representative prior art plastic extruding technique.
The thickness of the applied plastic coating or sheath is such that the outside diameter of the composite strand is preferably from at least about 0.200 inch to about 0.750 inch.
In one aspect, the present invention relates to the use of a composite strand as described above in the metal and plastic fence system of my earlier filed co-pending application. In another aspect, the invention relates to a fence system wherein a plurality of composite strands extend between a plurality of fence posts to create a highly visible, safe and attractive barrier particularly well suited for livestock confinement.
The present invention contemplates a variety of cross-sectional shapes for the composite strand. For example, the plastic sheath or coating may be applied so as to impart to the overall strand a circular, oval, or semicircular cross-section, but other shapes may be employed with equal effectiveness.
It is also a feature of this invention that the composite strand be electrically non-conductive, conductive, or selectively conductive. In accordance with the invention, the composite strand may be made conductive by the addition of carbon black particles to the plastic sheath composition prior to extrusion, or by co-extruding a conductive stripe on the surface of the plastic sheath. Other methods, well known in the art, may also be employed.
The composite strand, of course, would preferably be predominantly white and the conductive stripe black. Nevertheless, other configurations are contemplated, such as black conductive stripes with a variety of other colors, fluorescent or non-fluorescent, reflective or non-reflective, etc., for enhancing visibility.
In another, related aspect, this invention relates to the use of fasteners for securing the coated wire to the fence post in such a manner that they are essentially prevented from any vertical movement within the confines of the fastener or bracket, but are permitted to move horizontally therein to compensate for expansion and/or contraction due to variations in temperature, and to allow tensioning of the wires at the end posts. Staple-type or other similar fastening hardware may be used, so long as the fasteners conform generally to the cross-sectional shape of the composite strand so as to substantially limit vertical displacement of the composite strands. Stop elements may be employed to limit penetration of the fasteners into the fence posts to ensure horizontal slidability of the composite strand.
It will be appreciated that the novel composite strand of this invention combines the high strength, low cost characteristics of wire with the high visibility, safety, and aesthetic features of wood.
Other objects and advantages attributable to the subject invention will be apparent from the detailed specification which follows.